Package org.apache.druid.segment.virtual

Class FallbackVirtualColumn

java.lang.Object

org.apache.druid.segment.virtual.FallbackVirtualColumn

All Implemented Interfaces:

Cacheable, VirtualColumn

public class FallbackVirtualColumn
extends Object
implements VirtualColumn

A virtual column that picks one column or another based on whether they exist. It walks through an array of DimensionSpecs finding and using the first column that actually exists. If it believes that none of them exist it YOLOs it with the first entry from the list.

If you are using this virtual column and want to have a decorator/extraction function on your DimensionSpec, it is expected that you will put it on the specs in the list rather than on the spec that references this virtual column. That is, when this virtual column resolves a dimension, it ignores the decoration from the spec that it was given and instead uses the spec as defined in the list as-is to delegate to the column that it chose.

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.druid.segment.VirtualColumn

VirtualColumn.EquivalenceKey

Constructor Summary

Constructors

Constructor	Description
FallbackVirtualColumn(String name, ArrayList<DimensionSpec> columns)

Method Summary

Modifier and Type	Method	Description
boolean	canVectorize(ColumnInspector inspector)
ColumnCapabilities	capabilities(String columnName)	This method is deprecated in favor of VirtualColumn.capabilities(ColumnInspector, String), which should be used whenever possible and can support virtual column implementations that need to inspect other columns as inputs.
ColumnCapabilities	capabilities(ColumnInspector inspector, String columnName)	Return the ColumnCapabilities which best describe the optimal selector to read from this virtual column.
byte[]	getCacheKey()	Get a byte array used as a cache key.
ArrayList<DimensionSpec>	getColumns()
ColumnIndexSupplier	getIndexSupplier(String columnName, ColumnIndexSelector indexSelector)	Get the ColumnIndexSupplier of the specified virtual column, with the assistance of a ColumnSelector to allow reading things from segments.
String	getOutputName()	Output name of this column.
ColumnValueSelector<?>	makeColumnValueSelector(String columnName, ColumnSelectorFactory factory)
DimensionSelector	makeDimensionSelector(DimensionSpec dimensionSpec, ColumnSelectorFactory factory)
MultiValueDimensionVectorSelector	makeMultiValueVectorDimensionSelector(DimensionSpec dimensionSpec, VectorColumnSelectorFactory factory)
SingleValueDimensionVectorSelector	makeSingleValueVectorDimensionSelector(DimensionSpec dimensionSpec, VectorColumnSelectorFactory factory)
VectorObjectSelector	makeVectorObjectSelector(String columnName, VectorColumnSelectorFactory factory)
VectorValueSelector	makeVectorValueSelector(String columnName, VectorColumnSelectorFactory factory)
List<String>	requiredColumns()	Returns a list of columns that this virtual column will access.
boolean	usesDotNotation()	Indicates that this virtual column can be referenced with dot notation.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface org.apache.druid.segment.VirtualColumn

getEquivalanceKey, makeColumnValueSelector, makeColumnValueSelector, makeDimensionSelector, makeDimensionSelector, makeGroupByVectorColumnSelector, makeMultiValueVectorDimensionSelector, makeMultiValueVectorDimensionSelector, makeSingleValueVectorDimensionSelector, makeSingleValueVectorDimensionSelector, makeVectorObjectSelector, makeVectorObjectSelector, makeVectorValueSelector, makeVectorValueSelector, toSelectableColumn

Constructor Details

FallbackVirtualColumn

public FallbackVirtualColumn(String name,
 ArrayList<DimensionSpec> columns)

Method Details

getOutputName

public String getOutputName()

Description copied from interface: VirtualColumn

Output name of this column.

Specified by:

getOutputName in interface VirtualColumn

Returns:

name

getColumns

public ArrayList<DimensionSpec> getColumns()

getCacheKey

public byte[] getCacheKey()

Description copied from interface: Cacheable

Get a byte array used as a cache key.

Specified by:

getCacheKey in interface Cacheable

Returns:

bytes to be used as cache key - or null if this object should not be cached.

makeDimensionSelector

public DimensionSelector makeDimensionSelector(DimensionSpec dimensionSpec,
 ColumnSelectorFactory factory)

Specified by:

makeDimensionSelector in interface VirtualColumn

makeColumnValueSelector

public ColumnValueSelector<?> makeColumnValueSelector(String columnName,
 ColumnSelectorFactory factory)

Specified by:

makeColumnValueSelector in interface VirtualColumn

canVectorize

public boolean canVectorize(ColumnInspector inspector)

Specified by:

canVectorize in interface VirtualColumn

makeSingleValueVectorDimensionSelector

public SingleValueDimensionVectorSelector makeSingleValueVectorDimensionSelector(DimensionSpec dimensionSpec,
 VectorColumnSelectorFactory factory)

Specified by:

makeSingleValueVectorDimensionSelector in interface VirtualColumn

makeMultiValueVectorDimensionSelector

public MultiValueDimensionVectorSelector makeMultiValueVectorDimensionSelector(DimensionSpec dimensionSpec,
 VectorColumnSelectorFactory factory)

Specified by:

makeMultiValueVectorDimensionSelector in interface VirtualColumn

makeVectorValueSelector

public VectorValueSelector makeVectorValueSelector(String columnName,
 VectorColumnSelectorFactory factory)

Specified by:

makeVectorValueSelector in interface VirtualColumn

makeVectorObjectSelector

public VectorObjectSelector makeVectorObjectSelector(String columnName,
 VectorColumnSelectorFactory factory)

Specified by:

makeVectorObjectSelector in interface VirtualColumn

capabilities

public ColumnCapabilities capabilities(String columnName)

Description copied from interface: VirtualColumn

This method is deprecated in favor of VirtualColumn.capabilities(ColumnInspector, String), which should be used whenever possible and can support virtual column implementations that need to inspect other columns as inputs. This is a fallback implementation to return the capabilities of this virtual column, which includes a type that corresponds to the best performing base selector supertype (e. g. BaseLongColumnValueSelector) of the object, returned from VirtualColumn.makeColumnValueSelector(String, ColumnSelectorFactory). May vary based on columnName if this column uses dot notation.

Specified by:

capabilities in interface VirtualColumn

Parameters:

columnName - the name this virtual column was referenced with

Returns:

capabilities, must not be null

capabilities

@Nullable
public ColumnCapabilities capabilities(ColumnInspector inspector,
 String columnName)

Description copied from interface: VirtualColumn

Return the ColumnCapabilities which best describe the optimal selector to read from this virtual column.

The ColumnInspector (most likely corresponding to an underlying ColumnSelectorFactory of a query) allows the virtual column to consider this information if necessary to compute its output type details.

Examples of this include the ExpressionVirtualColumn, which takes input from other columns and uses the ColumnInspector to infer the output type of expressions based on the types of the inputs.

Specified by:

capabilities in interface VirtualColumn

Parameters:

inspector - column inspector to provide additional information of other available columns

columnName - the name this virtual column was referenced with

Returns:

capabilities, or null if the column should be treated as if it doesn't exist.

requiredColumns

public List<String> requiredColumns()

Description copied from interface: VirtualColumn

Returns a list of columns that this virtual column will access. This may include the names of other virtual columns. May be empty if a virtual column doesn't access any underlying columns. Does not pass columnName because there is an assumption that the list of columns needed by a dot-notation supporting virtual column will not vary based on the columnName.

Specified by:

requiredColumns in interface VirtualColumn

Returns:

column names

usesDotNotation

public boolean usesDotNotation()

Description copied from interface: VirtualColumn

Indicates that this virtual column can be referenced with dot notation. For example, a virtual column named "foo" could be referred to as "foo.bar" with the Cursor it is registered with. In that case, init will be called with columnName "foo.bar" rather than "foo".

Specified by:

usesDotNotation in interface VirtualColumn

Returns:

whether to use dot notation

getIndexSupplier

@Nullable
public ColumnIndexSupplier getIndexSupplier(String columnName,
 ColumnIndexSelector indexSelector)

Description copied from interface: VirtualColumn

Get the ColumnIndexSupplier of the specified virtual column, with the assistance of a ColumnSelector to allow reading things from segments. Returns null if the virtual column wants to act like a missing column. Returns NoIndexesColumnIndexSupplier.getInstance() if the virtual column does not support indexes and wants cursor-based filtering.

Specified by:

getIndexSupplier in interface VirtualColumn